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How Hyper-V storage migration has improved in version 3.0

Storage expert Brien Posey compares VMware Storage vMotion and Hyper-V Live Storage Migration, with a look at how they work.

Is Live Storage Migration in Hyper-V essentially the same thing as Storage vMotion in VMware environments? How does storage migration in Hyper-V work?

Yes, Hyper-V's Live Storage Migration is essentially the same thing as VMware's Storage vMotion. For those who might not be familiar with these features, VMware's Storage vMotion allows you to migrate virtual machine disk files across storage arrays with no interruption of service. In other words, if a physical storage device begins to run low on space, a virtual machine can be moved to a different (presumably larger) storage device while the virtual machine is running, with no interruption in service. Hyper-V 3.0's Live Storage Migration will accomplish the same thing.

If this type of Hyper-V storage migration functionality sounds familiar, it is likely because the Windows Server 2008 R2 version of Hyper-V offered a similar feature called Quick Storage Migration. But Quick Storage Migration differed from Live Storage Migration in that it required a brief storage interruption. The migration process required the virtual machine to be put into a saved state for about a minute while its memory state and differencing disks were migrated.

The functionality that makes Live Storage Migrations possible in Hyper-V is relatively simple. When Live Storage Migration is initiated, disk reads and writes are still made against the source virtual hard disk. While these read and write operations are occurring, the virtual hard disk's contents are copied to the new destination as a background operation. Once the copy process is complete, write operations are mirrored to both the source and destination virtual hard disks. This allows any outstanding write operations to be completed. After the source and destination virtual hard disks are synchronized, the virtual machine is switched over to use the destination virtual hard disk, and the source virtual hard disk is deleted.

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